The Oxford comma is just a pretentious term for the simple, but hard-working, serial comma (also known as a series comma, or less respectfully as the “extra comma” or the “optional comma”) that is placed before a coordinating conjunction (generally and, or, or nor) at the end of a list of three or more items. But why is it called the Oxford comma? According to the esteemed editors of the Oxford English Dictionary who know a thing or two about the English lexicon, it is called the Oxford comma because it was the style indicated in the Oxford Manual of Style published in 1905. Since then the Oxford comma has been consistently used by the editors, readers, and printers at Oxford Univesity Press for more than 100 years. So there you have it.
For those who feel superior to the British — because, after all, America did win the Revolutionary War — it was important to ditch this Anglophilic term in favor of a more American term. Understandably, one of America’s oldest and most respected universities is Harvard University; thus it was fitting to call it the Harvard comma (apparently other venerable American universities were unaware that the lowly serial comma’s name was up for grabs). However, to be fair, it could have easily been called the Yale comma, or the Stanford comma. In the English language — to paraphrase a legal maxim — usage is 9/10ths of the law — thus, the Harvard comma endures.
The use of the serial comma is as divided as Congress. The editors of the leading style guides — Oxford University Press Style Manual, Fowler’s Modern English Usage, and The Chicago Manual of Style — all favor the serial comma. The Associated Press Stylebook, on the other hand, favors not using the serial comma. The two main arguments in favor of the serial comma is its traditional usage for more than a century and that, in most cases, it resolves ambiguity. Across the aisle, the anti-serial comma contingent argues that the modern practice is not using the serial comma because it is redundant — and get this: it may introduce ambiguity. This is starting to sound just like the Congressional drivel coming out of D.C…
For grammar pedants (perhaps some who suffer from obsessive-compulsive disorder) there is absolutely no middle ground: the use (or avoidance) of the serial comma can lead to a fierce debate full of name-calling, nasty epithets, and caterwauling — leaving most bystanders, um, comatose. Most level-headed English teachers, however, advocate the simplest strategy — use common sense. Does the serial comma clarify the sentence?
For further reading: oxforddictionaries.com/us/words/what-is-the-oxford-comma